Dry Block Calibrator with Improved Temperature Field and Integrated Fixed-Point Cells

To reduce uncertainty of calibrations of contact thermometers using dry block calibrators, a concept was developed at Institute for Process Measurement and Sensor Technology of Technische Universität Ilmenau. This concept uses a multi-zone heating, heat flux sensors and a multiple fixed-point cell. The paper shows the concept and its validation on the basis of a dry block calibrator with a working temperature range of \(70\,^{\circ }\hbox {C}\) to \(430\,^{\circ }\hbox {C}\). The experimental results show a stability of \({\pm } 4\,\hbox {mK}\) for the reference temperature and axial temperature differences in the normalization block less than \({\pm }55\,\hbox {mK}\).     

Multiple Fixed-Point Cell

The paper describes the construction and investigation of multiple fixed-point cells usable for the calibration of thermocouples at temperatures above 1100  \(^{\circ }\) C. These fixed-point cells made of pure graphite are characterized by a simple construction as well as by a flexible application. The cylindrical basic mount is equipped with a central hole for the insertion of a thermocouple, and with eight drill holes containing exchangeable cartridges which surround the central bore axially symmetrically. The cartridges are filled with different metal–carbon (Me–C) eutectics: cobalt–carbon (Co–C), nickel–carbon (Ni–C), palladium–carbon (Pd–C), and rhodium–carbon (Rh–C). The melting temperatures of the different Me–C eutectics of the cartridges were compared to the melting temperatures of commonly used Me–C eutectic fixed-point cells of the Physikalisch-Technische Bundesanstalt by using a Pt/Pd thermocouple (Co–C, Ni–C) and Type B thermocouples (Pd–C, Rh–C). The uncertainties ( \(k = 2\) ) of the emfs measured at the inflection points of the melting curves are in the order of a few \(\upmu \) V which correspond to temperature equivalents between 0.3 K and 0.6 K. Furthermore, the difference between the melting temperatures of the Co–C and Ni–C cartridges was found to be 4.2 K by using simultaneously two sets of four cartridges filled with the two materials and placed alternately in the eight outer holes of one basic mount.     

局部放电校准器标准测量系统的研制及校验

局部放电电荷量是国际计量局电磁计量领域校准测量能力的关键参数。在进行高压试品局部放电量的检测中,需首先用局部放电校准器对整个高压回路进行标定,局部放电校准器所复现的电荷量是局部放电测量准确与否的重要保证。通过理论推导和测量线路仿真,分析了局部放电校准器源内阻、连接电缆和积分电阻对积分波形和测量结果的影响。通过修正测量系统各档位积分系数,独立开发了自动化测量软件并将测量系统整体溯源到直流电流和时间参数。能力验证结果表明该测量系统满足参考电荷量测量仪准确度等级的要求。     

Cryostat for Fixed-Point Calibration of Capsule-Type SPRTs

A cryostat for fixed-point calibration of capsule-type SPRTs (standard platinum resistance thermometers) was developed. Using this system, cryogenic fixed points defined on the International Temperature Scale of 1990 (ITS-90) were realized. The cryogenic cells were argon, oxygen, neon, and two equilibrium-hydrogen (e-H₂) cells, made by INRiM, Italy. The uncertainty of the realization of each fixed point was estimated to range from 0.53 mK to 0.43 mK (k = 2). The realizations of the triple point of e-H₂ using two sealed cells coincided within 0.1 mK. Therefore, we are able to calibrate capsule-type SPRTs down to 24.5561 K within an uncertainty of 1 mK (k = 2) by this system. A closed-cycle helium gas refrigerator was used for the cryostat. Each sealed cell was designed so that it could accommodate three sealed cells in the thermometer wells made within the cell. Therefore, the cryostat was designed to accommodate only one sealed cell at a time. The base temperature of this liquid-free cryostat, when one sealed cell and three capsule-type SPRTs were attached for calibration, was ~17 K. For the realization of the triple point of e-H₂, we used liquid helium for additional cooling. Adiabatic melting of the triple point was realized by controlling the inner-most radiation shield at a temperature very close to that of the triple point, and by applying a heat pulse by a heater directly wound to the cell. The amount of the heater power and the waiting time for the thermal equilibrium after each heat pulse were chosen in a way that the adiabatic melting could be finished within ~6 h for each cell. The triple point of each cryogenic fixed point was deduced from the equilibrium temperatures between the heat pulses and subsequent extrapolation to the liquidus point. For the oxygen cell, temperatures of two solid?Csolid transitions (???C?? and ???C?? transitions) were also measured, and the results were consistent with values reported in the literature within the designated uncertainty.     

Fixed-Point Comparison Uncertainties for Two Cell Geometries

To realize the ITS-90 according to its definition, among others, the melting and freezing temperatures of ideally pure metals are needed. Therefore, many national metrology institutes (NMIs) utilize a group of cells instead of one single cell as the national reference for each temperature. With direct fixed-point cell comparisons on a regular basis, it is feasible to account for the small differences between the individual fixed-point temperatures and to detect possible temperature drifts of the cells. At PTB (the German NMI), in recent years, these groups of national standard cells and the so-called transfer cells for calibrations have been complemented by newly developed slim fixed points. These cells typically contain 75% to 80% less fixed-point material compared with standard cells. Slim cells are used for homogeneity investigations of large batches of fixed-point material, for doping experiments to determine the influence of very small amounts of impurities on the fixed-point temperature with very small uncertainties, and for the investigation of contamination or purification effects after the manufacture of a fixed-point cell. These investigations have shown that the main limitation of slim cells is the quality of the phase boundary. The small dimensions of the cell do not allow the formation of a closed phase boundary (or even two of them). However, this can be compensated using a quasi-adiabatic realization procedure, and in this way, uncertainties comparable to those of standard fixed-point cells can be achieved. In this article, the design of the cells as well as typical measurement results and uncertainties for the direct comparison of fixed-point cells of both types, the standard size and slim design, are presented.     

Some Curious Results with a Gallium Fixed-Point Cell

In 2009, most of the gallium fixed-point cells in use in different INRIM laboratories were compared with Italy??s national standard. The comparison has uncovered problems with one of the commercial devices, realizing a temperature about 0.7 mK too low which initially was even changing linearly with time. An additional series of measurements was undertaken to find out the reason for this behavior, but not being allowed to open the cell, only a suspicion on the possible cause has remained. A way is suggested that might give users an indication of such misbehavior of their cell. The results underline the importance for those NMIs with only a single cell, for any fixed point, to undertake regular comparisons with another cell as a check on its behavior.     

标准太阳电池标定值计量方法研究

基于差分光谱响应度法搭建了标准太阳电池标定值校准装置,分析了标准太阳电池绝对光谱响应度随电池温度和偏置光辐照度的变化关系,通过数值拟合得到太阳电池短路电流与偏置电流的关系,实现太阳电池标定值测量不确定度1.2%(k=2)。搭建了标准太阳电池标定值户外计量装置,实现测量不确定度2.38%(k=2)。差分光谱响应度法与户外总辐射法测量结果比对的比率值为0.95,表明2种方法测量结果在不确定范围内量值等效。     

基于温度校准的数字压力校验仪的设计和实现

针对现场测试需求,将标准温度作为压力补偿模型的影响量来源,设计了基于温度校准的数字压力校验仪。校验仪利用上位机程序获得标准温度和内置温度传感器输出值对应列表,建立温度修正模型,确保参与压力显示的温度引入量准确,能有效降低温度传感器漂移带来的影响。     

过程校验仪热电偶功能校准方法分析

通常对过程校验仪中具有参考端温度自动补偿的热电偶功能的校准方法常用的有温度校准器法、0℃恒温器法、恒温槽法等三种,文中对参考端温度自动补偿原理和三种校准方法进行了分析。     

High-Temperature Fixed-Point Facilities for Improved Thermocouple Calibration—Euromet Project 857

LNE, NPL, and PTB decided in 2005 to join their research efforts in the framework of Euromet Project 857 with the aim of reducing the calibration uncertainty of noble metal and other high-temperature thermocouples by at least a factor of two. This ambitious target will be met through the development and implementation of robust high-temperature fixed points based on metal–carbon eutectic technology. The Euromet project is structured around five work packages and ensures good and efficient cooperation between the partners to meet the objectives within the project timeframe of four years. Furthermore, a formal cooperative research agreement has been established with the National Metrology Institute of Japan (NMIJ) to demonstrate, on a worldwide basis, that this new method is a significant improvement over current calibration methods. In summary, the project consists of (a) the development of sets of cells at the cobalt–carbon eutectic point (1324^◦C) and palladium–carbon eutectic point (1492^◦C) and (b) the construction of platinum/palladium (Pt/Pd) thermocouples carefully stabilized for use to these temperatures. Supplementary research to be undertaken as part of this project is the improvement of fixed-point construction and realization capabilities through high-temperature furnaces with low thermal gradients. This paper describes the European project and gives an overview of current progress.     

光伏标准电池室外一级标定的不确定度分析

利用拉萨地区较好的阳光辐射条件,采用室外直接辐照度标定方法建立了标准光伏电池一级标定试验平台,提出了一级标定试验的实验条件及方法。对一级标定试验入射光辐照度、光谱失配修正、电池短路电流及温度等参数进行了不确定度分析及评定,标定结果具有较高的参考价值。室外一级标定采用绝对辐射计溯源至世界辐射基准,测量结果准确可靠,且具有较好的复现性。     

Calibration of an Absolute Radiation Thermometer for Accurate Determination of Fixed-Point Temperatures

For accurate determinations of thermodynamic temperature, NPL has developed its absolute radiation thermometer (ART), which is calibrated traceably against a cryogenic radiometer. This article reviews some of the potential sources of systematic uncertainty present in the calibration and use of ART. In particular, this article is concerned with the evaluation of the size-of-source effect and the lens transmittance, as well as potential differences in the responsivity of a transfer trap detector when calibrated in terms of radiant power and used in irradiance mode.     

Melting Temperatures of Eutectic Fixed-Point Cells Usable for the Calibration of Contact Thermometers

The objective of the present investigation was the determination of the melting temperatures of the eutectic compounds Fe–C, Co–C, and Ni–C. Six eutectic fixed-point cells of the Physikalisch-Technische Bundesanstalt (PTB) (Fe–C1, Fe–C2, Co–C1, Co–C2, Ni–C1, and Ni–C2) and two cells of the Brazilian National Metrological Institute (Inmetro) (Fe–C1V and Ni–C1V), useable for the calibration of contact thermometers, were investigated. Their melting temperatures were calculated by extrapolation of the emf-temperature characteristics of four stable Pt/Pd thermocouples, which were calibrated at the eutectic fixed points and at conventional fixed points of the International Temperature Scale of 1990 (ITS-90). On the basis of the eight eutectic fixed-point cells and seven independent calibration runs, the melting temperatures of the Fe–C, Co–C, and Ni–C eutectics resulted in 1153.67 ± 0.15°C, 1323.81 ± 0.27°C, and 1328.48 ± 0.20°C, respectively, with expanded uncertainties corresponding to a coverage factor of k = 2.     

Indirect Determination of the Thermodynamic Temperature of a Gold Fixed-Point Cell

Since the value T ₉₀(Au) was fixed on the ITS-90, some determinations of the thermodynamic temperature of the gold point have been performed which form, with other renormalized results of previous measurements by radiation thermometry, the basis for the current best estimates of (T ? T ₉₀)_Au = 39.9 mK as elaborated by the CCT-WG4. Such a value, even if consistent with the behavior of T ? T ₉₀ differences at lower temperatures, is quite influenced by the low values of T _Au as determined with few radiometric measurements. At INRIM, an independent indirect determination of the thermodynamic temperature of gold was performed by means of a radiation thermometry approach. A fixed-point technique was used to realize approximated thermodynamic scales from the Zn point up to the Cu point. A Si-based standard radiation thermometer working at 900 nm and 950 nm was used. The low uncertainty presently associated to the thermodynamic temperature of fixed points and the accuracy of INRIM realizations, allowed scales with an uncertainty lower than 0.03 K in terms of the thermodynamic temperature to be realized. A fixed-point cell filled with gold, 99.999 % in purity, was measured, and its freezing temperature was determined by both interpolation and extrapolation. An average T _Au = 1337.395 K was found with a combined standard uncertainty of 23 mK. Such a value is 25 mK higher than the presently available value as derived by the CCT-WG4 value of (T ? T ₉₀)_Au = 39.9 mK.     

Calibration of a Novel MEMS Inertial Reference Unit

This paper describes a novel low-cost inertial reference unit (IRU) developed for spin-stabilized sounding rockets, as well as a method to calibrate the IRU using a one-axis rate table. The IRU contains three orthogonally mounted microelectromechanical system (MEMS) gyros and is intended for use in a low-cost system for attitude determination of sounding rockets. The high spin velocity of the rockets (4–6 r/s) causes sensor misalignments and scale factor errors to have a large effect on the gyro outputs. The performance of the IRU is considerably improved by detailed calibration, including temperature compensation. For sounding rocket applications, the total rate error is typically reduced by more than one order of magnitude. The calibration procedure uses a ramp profile calibration maneuver input at all three sensor axes and a Kalman filter to estimate the 12 error parameters.      

Establishment of the Co-C Eutectic Fixed-Point Cell for Thermocouple Calibrations at NIMT

In 2015, NIMT first established a Co-C eutectic temperature reference (fixed-point) cell measurement capability for thermocouple calibration to support the requirements of Thailand’s heavy industries and secondary laboratories. The Co-C eutectic fixed-point cell is a facility transferred from NPL, where the design was developed through European and UK national measurement system projects. In this paper, we describe the establishment of a Co-C eutectic fixed-point cell for thermocouple calibration at NIMT. This paper demonstrates achievement of the required furnace uniformity, the Co-C plateau realization and the comparison data between NIMT and NPL Co-C cells by using the same standard Pt/Pd thermocouple, demonstrating traceability. The NIMT measurement capability for noble metal type thermocouples at the new Co-C eutectic fixed point (\(1324.06\,{^{\circ }}\hbox {C}\)) is estimated to be within \(\pm 0.60\,\hbox {K}\) (\(k=2\)). This meets the needs of Thailand’s high-temperature thermocouple users—for which previously there has been no traceable calibration facility.     

Pulsed Wavemeter Timing Reference for Sampling Oscilloscope Calibration

A pulsed wavemeter technique is described that is useful as a source of microwave frequency sine waves for the time base calibration of sampling oscilloscopes.